This invention relates generally to fiber optic systems and, more particularly, to a distortion compensated fiber optic system and a method for accomplishing substantially distortion free electromagnetic radiation transmission through an optical fiber.
Optical fibers that act in the capacity of "light pipes" have been available for a number of years, finding utility in a variety of ways such as in medical instruments, photocopying machines, and air plane, space shuttle, automobile instrument panels, etc. The potential of large bandwidth and small size in optical fibers has, in recent years, led to the feasibility of optical communication systems. In fact, during the past few years the use of optical fibers has grown mainly because of their potential application as transmission media in long-distance, high-bit-rate optical communication systems. With the advent of the single-mode optical fiber, that is, a fiber which is capable of eliminating the propagation of all but one electromagnetic mode, the use of optical fibers (and especially single-mode optical fibers) has increased.
Recently, considerable attention has been given to the study of pulse distortions in single-mode optical fibers where the maximum data rate of signal transmission is limited by the group velocity dispersion (GVD). Distortion-free pulse propagation has been demonstrated in fused silica fibers at 1.3 .mu.m and in the 1.3-1.7 .mu.m spectral region, where the GVD of a single fiber or a combination of two fibers, respectively, vanishes. Unfortunately, in spectral regions other than the 1.3-1.7 .mu.m region set forth above, transmission through such single-mode optical fibers is subject to substantial distortion. It would therefore be highly desirable to expand the wavelength region of distortion-free pulse propagation towards shorter wavelengths (visible, in particular) where the group velocity dispersion is particularly large.
Recent work in this area, as exemplified by H. Nakatsuka and D. Grischkowsky, Opt. Lett., Vol. 6, January 1981, pgs 13-15, has provided evidence that the use of an atomic-sodium vapor delay line can cause the recompression of light pulses broadened by passage through optical fibers. Although this type of optical fiber system has increased the effective spectral range of optical fibers associated with gaseous systems, its general use is severely limited. For example, as a result of its considerable bulkiness, complexity and sensitivity to surrounding conditions such optical systems are unable to be easily transported or be used in the field. Therefore, there still exists a substantial need for reliable and effective distortion compensated fiber optic systems.